In semiconductor devices, polyimide resins having excellent heat resistance and electrical properties as well as excellent mechanical properties have conventionally been used in surface protecting films and interlayer insulating layers. In recent years, as the integration degree of semiconductor devices is increasing and the size thereof is increasing, there are increasing demands on resin encapsulation packages to be reduced in thickness or size. For meeting these demands, surface mount modes such as LOC (lead on chip) or solder reflow are employed. Consequently, there are increasing demands on a polyimide resin to have more suitable properties as a protective film on the uppermost surface of a semiconductor circuit. That is, a polyimide resin is now becoming to be required to have better mechanical properties and heat resistance.
On the other hand, also coming into use is a photosensitive polyimide which is a polyimide resin having sensitivity properties, and which has a feature such that it can simplify the step of forming a pattern to shorten the cumbersome fabrication process.
Heat-resistant photoresists using the conventional photosensitive polyimide or a precursor thereof have been well known. Examples of negative photosensitive resins include those obtained by introducing a methacryloyl group into a polyimide precursor through an ester linkage or an ionic bond (for example, see Patent Documents 1 to 4), a soluble polyimide having photopolymerizable olefin (for example, see Patent Documents 5 to 10), and a self-sensitizing polyimide having a benzophenone skeleton and having an alkyl group at the ortho-position of the aromatic ring to which a nitrogen atom is bonded (for example, see Patent Documents 11 and 12). The uses thereof are also well known. However, the aforementioned negative photosensitive resins needs an organic solvent, such as N-methylpyrrolidone, upon development. Therefore, there has been proposed a positive photosensitive resin which can be developed with an alkaline aqueous solution.
As positive photosensitive resins, there are known a positive photosensitive resin obtained by, for example, a method in which an o-nitrobenzyl group is introduced into a polyimide precursor through an ester linkage (for example, see Non-patent Document 1), a method in which a naphthoquinonediazide compound is mixed into soluble hydroxylimide or a polyoxazole precursor (for example, see Patent Documents 13 and 14), or a method in which naphthoquinonediazide is introduced into soluble polyimide through an ester linkage (for example, see Non-patent Document 2). There are also known a photosensitive resin composition obtained by mixing naphthoquinonediazide into a polyimide precursor (for example, see Patent Document 15).
The negative photosensitive resins have a problem of poor resolution due to light-absorption wavelength of its sensitizer. In some applications, the resins also cause a problem of low yield in the production. Further, because of the limitation in the structure of the polymer used in the polyimide resin, the physical properties of the finally-obtained film are also limited, which makes the resins unsuitable for multipurpose use. Like the negative photosensitive resins, the positive photosensitive resins have similar problems of the low sensitivity or resolution due to the problem of the light-absorption wavelength of its sensitizer, and that the structure of polymer is limited.
There have been proposed materials having introduced a phenolic hydroxyl group instead of carboxylic acid, such as a material obtained by mixing a diazonaphthoquinone compound into a polybenzoxazole precursor (for example, see Patent Document 16), and a material obtained by introducing a phenolic site into polyamide acid through an ester linkage (for example, see Patent Document 17), but development properties of these materials are unsatisfactory. Further, they have problems of reduction in thickness of the unexposed portion, and peeling-off of the resin from the substrate.
For improving the development properties and the adhesion properties, there has been proposed a material containing polyamide acid having a siloxane site in the polymer skeleton (for example, see Patent Documents 18 and 19), but this material has poor storage stability due to the polyamide acid contained therein. For improving the storage stability and the adhesion property, a material having an amine end group capped with a polymerizable group has been proposed (for example, see Patent Documents 20 to 22). However, these materials use a diazoquinone compound containing a number of aromatic rings as an acid generator and hence have poor sensitivity. Further, because of the high content of the diazoquinone compound, the film after heat-curing results in having considerably low mechanical properties, which makes it difficult to practically use the materials.
For solving the above problems bound to the diazoquinone compound, materials to which a variety of chemical amplification systems is applied have been proposed. Examples thereof include chemically amplified polyimide (for example, see Patent Document 23), and chemically amplified polyimide and polybenzoxazole precursor (for example, see Patent Documents 24 to 30). However, among these, the material having high sensitivity has a low molecular weight, and hence has low film properties. On the other hand, the material having excellent film properties has a high molecular weight, and hence has unsatisfactory solubility and low sensitivity. Therefore, any of these materials are not practical, and materials which can be put into practical use have not yet been obtained.